1. field of the Invention PA1 2. Description of the Prior Art
This invention relates to a process for preparing .alpha.-formyl sulfides and 2-hydrocarbylthioaldoximes therefrom.
A process for the preparation of 2-hydrocarbylthioaldoxime compounds has been suggested by U.S. Pat. No. 3,217,036 (issued 1965 to Payne). An example of such compounds is 2-methyl-2-methylthiopropionaldoxime, which is useful as a nematocide as well as for preparing 2-methyl-2-methylthiopropionaldehyde-N-methylcarbamoyloxime which is useful as a pesticide. It is suggested in the said United States patent to prepare the 2-methylthioaldoxime by reacting in an organic solvent methylmercaptan in the presence of a base with the azodioxy-coupled dimer of 1-nitroso-2-chloro-2-methylpropane. The dimer may be prepared by the reaction of isobutylene with nitrosyl chloride or the combination of sodium nitrite and hydrochloric acid.
The process of Payne has its drawbacks in that the dimer is unstable (explosive) at elevated temperatures and the reported yields have been relatively low.
It has also been suggested by Kirrmann et al., (Chemical Abstracts 61:8180a) to react in anhydrous ether certain .alpha.-chloroaldehydes, including .alpha.-chloroisobutyraldehyde, with sodium thiomethylate to give .alpha.-(methylthio)aldehyde, but in yields in the range of 55 to 80%. Besides the low yields, the necessity for carrying out the reaction in anhydrous ether requires a costly purification or wastage of the solvent.
It has been additionally suggested in U.S. Pat. No. 3,419,617 (issued 1968 to Doss) to form .alpha.-formyl sulfides by reacting .alpha.-haloaldehydes with a thiol in the presence of pyridine and derivatives thereof. The suggested process also has its drawbacks as pyridine and its derivatives are normally too impure following reaction to recycle, thereby increasing processing costs. Doss discloses that the desired reaction does not occur in the presence of water.